This occurred to me on my drive in this morning (I get lots of weird things running through my head). There’s no real need to have two forks to produce a single ring tone – you can do it with a simple bar with a support. It would be easier to fabricate and to tune, and you wouldn’t have the potential problem of the two arms getting slightly out of calibration with each other and causing “beats”. The existing design seem,s unnecessarily complex.
It’s apparently based on the use at first of a REAL fork, but eventually Musician John Shore in the 18th century designed one precisely for the use of tuning and called it a “pitch fork” (Was he being humorous, as one site suggests, or did the alternate meaning not exist in so well-known a way?). So the existing design developed from experience with existing forks, which were copied. But that doesn’t mean it’s the best design. Neveretheless, the double-fork design continues to be used in watches and gyroscopes, which implies that it IS a desirable shape.
But a quick internet search doesn’t reveal how or why the tuning fork is made that way, instead of people using end-supported bars or simply-supported “glockenspiel”-type arrangements (which would be a bit clumsier, but more straightforward in their physics and easier to tune). Nor can I find anything about Normal Modes of tuning forks.
So howcum tuning forks have that characteristic shape?
The Wiki page on tuning forks gives some information, but searching elsewhere I could find no explaination.
My WAG is that:
The vibrations from each tine interact with each other causing a harmonic feedback effect that reverberates the tone.
The shape is unique in that an unrestricted tone can be acquired from an unmounted object as opposed to a single tine having to be mounted or suspended.
1.) Not sure what you mean by that. As I think about it more, it seems to me that the two arms will be coupled oscillators, and so, rather than getting beats, you’ll get a mode at about the average of the two arms and one at about half the difference. That might agree with what you said.
2.) But if you cut off one of the arms of a tuning fork you’d have something that rang just as well – it’s not going to not “ring” just because it’s lacking one arm. That’s one of the things I proposed – a large and somewhat heavy bar supported at oneend as the full tuning fork is. You might argue that the center of mass will move more with a one-armed fork, but the distance and momentum of that move is so trivial that I can’t see it as a real reason to fabricate the forks in this way.
I think that may be why the tines are (more or less) the same length. If each tine oscillates at, say, 440Hz then the average will be 440 and the harmonic will be 0 (half the difference). If one tine oscillates at 400 and the other oscillates at 480 the average tone will still be 440 but the harmonic will be 40Hz. This would have an affect on the original tone’s amplitude and it would degrade quicker.
Not really, if you cut off one of the arms of a tuning fork you’d have something that resembled a crooked metal rod. It would reverberate only if mounted or suspended in such a way that did not dampen the vibration. If I held it in my hand, my hand would absorb the vibration but if it was mounted on something like rubber or suspended it would ring. A normal tuning fork is one piece of metal but still reverberates when held by the base.
Or I might not. I agree that the movement of the C. O. M. would be trivial.
Again, I have no cites for any of this other than direct experience with tuning forks, harmonics and such as a musician. I certainly don’t have the relevant math handy.
I very heartily disagree. The result would vibrate just fine. My hand doesn’t absorb the vibration of an exuisting tuning fork – it wouldn’t do it if I cut off that other arm. (NOT the handle, I insist, but the other of the two identical arms of the fork. If you disdagree, tell my why my hand doesn’t dampen it with both arms in place)
I’m pretty sure a two-armed tuning fork will ring for considerably longer than a single bar - the arms are opening and closing against each other, resulting in zero net movement at the point where they join the handle, therefore there’s no damping - with a single bar, the whole thing will try to resonate, including the bit you’re holding.
-If you cut off one of the arms, there’s no way the thing can resonate in a balanced way without transmitting a lot of the energy down the handle - it’s still possible to find places to hold a resonating single bar without damping it (glockenspiel bars are supported at specific points - I think they’re called nodes)
There are indeed. In fact, they define the nodes. And I know what you’re saying, but a long and heavy bar will vibrate with one end embedded in a wall. It would also vibrate if you throw it in the air and don’t restrict any point at all. It’s not necessary to have a stationary point held still for the bar to vibrate. A bar ought to be free to vibrate in the same way with your hand holding iot at one end instead of a rigid support. But perhaps I’m wrong, and your hand will not be stable enough for this.
I can’t find an online slow-motion video of a tuning fork (although the balanced reciprocal oscillation is very easily observed by merely building a very large tuning fork - which has a low frequency.
I did find this video of a wineglass resonating (and in fact it would not be at all inappropriate to think of the tuning fork as merely being a thin slice of the wineglass):
Yeah, that’s what I was trying to convey. The two arms reverberate. If one of the arms was shorter two things would happen - The conflicting frequencies would be detrimental to each other and the handle would absorb some of the vibration. If one of the arms were missing the handle would absorbe all of the vibration.
That’s the crux of the matter, I believe - humans are by far too squashy and floppy to be able to hold a simple resonating bar at one end. It’s the same thing with the king of primary school percussion instruments - the triangle - if you hold it with your hand, it just goes tink, not ting.
With no / minimal restriction a metal bar will vibrate freely (depending on it’s material) but when restriction is added the propertys of the restrictor must affect the vibrations. If you place the heavy bar in a tight vise it will resonate, if you wrap a rag around the bar and replace it in the tight vise the best you will get is a metalic thud.
Of course in both cases the bar will vibrate. But it will not resonate (sustain vibration) if the vibrations are absorbed in any way.
I don’t think this has been raised yet…getting a tuning fork resonating is only half of the problem. The sound also needs to be successfully transmitted to a larger resonator, whether a table top, a piano lid, a violin bridge or whatever. I presume the symmetrical shape of the tuning fork means the motion is converted to a (very small) vertical motion through the stem, small enough and in a direction which isn’t snuffed out immediately by the hand holding it.
Edit: yeah, I’ve got one I’m happy to cut off (I’ve never needed to use middle C and no idea where it came from!) I’ll just need to remember about it this evening, I’m not going to start doing it now
I always wondered what one did after one string was perfectly tuned per the tuning fork. Is it assumed that one who tunes an instrument has perfect pitch? And if so, then why does one need the tuning fork to start with?
Once one string is tuned, you can play a different note on it - the note to which one of the other strings should be tuned and thus tune the instrument against itself. Well, you can if it’s a guitar, not a harp.
My understanding is that most piano tuners do have some sort of perfect pitch. As far as I can remember from a previous thread on this, this would most likely be relative pitch. As I understand it, this means that they couldn’t necessarily hear a note and say “that’s an F#”, but given that F#, they could then pitch other notes accurately. Hence the need for the tuning fork to get the initial note right, before using this as a baseline to tune all the others.
Please could someone more knowledgable correct me if I’m wrong!
Perfect pitch and relative pitch are different. Perfect pitch is the ability to either recognize a pitch with no outside reference (passive perfect pitch) or produce a precise pitch without reference (active perfect pitch). Relative pitch is the ability to recognize and produce differences between pitches.
Relative pitch is a critical skill for any musician. Perfect pitch is useful, but far from critical, and can in fact be detrimental in some contexts.
Piano tuners tend to have particularly well developed relative pitch, giving them the ability to detect extremely small gradations of pitch.
